Novel photoreceptor-specific promoters for gene therapy in mid- to late-stage retinal degeneration

Inherited retinal degenerations (IRDs) cause progressive photoreceptor loss, leading to vision impairment. Gene therapy using adeno-associated viral (AAV) vectors holds immense promise for treating these conditions. However, achieving optimal gene expression at mid to late stages of retinal degeneration remains challenging due to scarcity of efficient photoreceptor-specific promoters expressed at these disease stages. This study aimed to identify and validate novel promoters capable of robust and specific transgene expression when ≥50% of photoreceptors are lost. Analysis of transcriptomic data from two naturally occurring canine IRD models, laser capture microdissection of retinal cryosections followed by qPCR, and RNA in situ hybridization identified six promising genes with sustained or upregulated expression in photoreceptors in late-stage disease. Upstream cis-regulatory elements of both canine and human orthologs were identified and characterized using in silico analyses and dual-luciferase assays. Short promoters (≤840 base pairs) derived from GNGT2, IMPG2, and PDE6H genes exhibited robust reporter gene expression in photoreceptors when delivered via AAV to the subretinal space of two non-allelic canine IRD models at mid and late disease stages. These findings provide a strategy to enhance AAV-mediated gene therapy by enabling sustained transgene expression in degenerating retinas, improving treatment outcomes for patients with progressive vision loss.